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Topic: 1986 Cougar 3.8 L won't idle. (Read 8985 times) previous topic - next topic

1986 Cougar 3.8 L won't idle.

Reply #15
Quote from: midnight cat;465390
I do know the fuel pressure is good. The psi is 35 or more which according to the shop manual is correct for a 1986 model. I will check with the mechanic to see if fuel is spraying when the engine is cranking. I don't think it is because if it was wouldn't the car start? The only way this car starts now is when starter fluid (or carb. cleaner) is sprayed directly into the TDI.

If fuel can be seen spraying while cranking the engine what does that indicate? Does that mean it's not getting enough fuel and that's why it needs alternate fuel as well to start?

1986 Cougar 3.8 L won't idle.

Reply #16
Per your previous post, the car runs just fine with the exception that it won't idle without your foot on the gas pedal?

1986 Cougar 3.8 L won't idle.

Reply #17
Quote from: JeremyB;465408
Per your previous post, the car runs just fine with the exception that it won't idle without your foot on the gas pedal?

Correct.

1986 Cougar 3.8 L won't idle.

Reply #18
Quote from: JeremyB;461926
Highly doubtful. TPS or ISC are my first thoughts, but get the KOEO and KOER codes to give you some better direction.

Quote from: JeremyB;462561
I had to look it up myself to make sure I wasn't forgetting things. Getting old!

ISC = Idle Speed Control. CFI's method to control idle. It physically moves the throttle blade to adjust airflow. IAC sends air through it and bypasses the throttle blades.


This...

You didn't indicate what the actual code that was thrown... Have you verified voltage at idle?


Although the 3.8 likes to blow head gaskets, the earlier ones aren't nearly as bad as the latter. Mine made it 226k before blowing.

Still my first thought. No offense, but not sure your mechanics have the background to solve the problem without just throwing parts at it.

1986 Cougar 3.8 L won't idle.

Reply #19
Quote from: JeremyB;465421
ISC = Idle Speed Control. CFI's method to control idle. It physically moves the throttle blade to adjust airflow. IAC sends air through it and bypasses the throttle blades.

I'm thinking if this were the case though it would be causing a deficiency in air delivery, not fuel delivery right? Spraying alternative fuel should have no effect if its a case of not enough air making it through the TV
--Steve
[thread=28690]1988 Cougar V6[/thread]
2012 F-150 3.7L
2011 Mustang 3.7L

1986 Cougar 3.8 L won't idle.

Reply #20
Derp. Yeah.

1986 Cougar 3.8 L won't idle.

Reply #21
Quote from: JeremyB;465421
Still my first thought. No offense, but not sure your mechanics have the background to solve the problem without just throwing parts at it.


I agree. I have lost confidence in the mechanics ability to diagnose as well. When I couldn't solve the problem myself I had the car towed to the mechanic because they had a reputation for working on Mustangs. Tomorrow they are replacing the idle speed control and rebuilding the throttle body (it was already rebuilt last summer) because we can't find a rebuilt TBI. I don't know if this will be fix the problem…I have my doubts. I can't keep dumping money into this car even though I've had it for 32 years. If I have to have it towed home I think I need to sell it.

1986 Cougar 3.8 L won't idle.

Reply #22
Quote from: JeremyB;465425
Derp. Yeah.

How does this car normally at start up get fuel to the injectors?  Does anyone have an answer to this question?

1986 Cougar 3.8 L won't idle.

Reply #23
The fuel pump powers up for a few seconds to prime the line when you turn on the key, then comes on again once you start cranking.  If you turn the key on, but don't crank the engine, you should hear it happening.

1986 Cougar 3.8 L won't idle.

Reply #24
Quote from: sarjxxx;465423
I'm thinking if this were the case though it would be causing a deficiency in air delivery, not fuel delivery right? Spraying alternative fuel should have no effect if its a case of not enough air making it through the TV
Not sure why I brain-freezed in my original reply.

Don't have the manual in front of me so I can't remember how it is supposed to function. The ISC has 4 pins. Power, +actuation (more throttle), -actuation (less throttle), and signal return which lets the ECU know the ISC is touching the throttle bracket (when the ISC touches the throttle bracket, a ground path is enabled. Might get some wonkiness if the ground isn't working. Or the TPS could be out of range. While cranking, WOT TPS voltage is a signal to not run the injectors to clear a flooded condition. The noid light results seem to refute that though.

A 'tired' injector might have issues responding to low idle pulse widths, but the've been replaced.
The fact that is runs fine while not idling should rule out fuel/spark availability - at least initially.

There is a powertrain/troubleshooting manual that should have proper procedures to run through - but I highly doubt they have one.

What is the lowest rpm that the engine will run in idle? What is the position/voltage of the ISC/TPS at this rpm? What happens when you drop below it?

1986 Cougar 3.8 L won't idle.

Reply #25
Quote from: TheFoeYouKnow;465433
The fuel pump powers up for a few seconds to prime the line when you turn on the key, then comes on again once you start cranking.  If you turn the key on, but don't crank the engine, you should hear it happening.

Ok thanks!

1986 Cougar 3.8 L won't idle.

Reply #26
Quote from: JeremyB;465436
Not sure why I brain-freezed in my original reply.

Don't have the manual in front of me so I can't remember how it is supposed to function. The ISC has 4 pins. Power, +actuation (more throttle), -actuation (less throttle), and signal return which lets the ECU know the ISC is touching the throttle bracket (when the ISC touches the throttle bracket, a ground path is enabled. Might get some wonkiness if the ground isn't working. Or the TPS could be out of range. While cranking, WOT TPS voltage is a signal to not run the injectors to clear a flooded condition. The noid light results seem to refute that though.

A 'tired' injector might have issues responding to low idle pulse widths, but the've been replaced.
The fact that is runs fine while not idling should rule out fuel/spark availability - at least initially.

There is a powertrain/troubleshooting manual that should have proper procedures to run through - but I highly doubt they have one.

What is the lowest rpm that the engine will run in idle? What is the position/voltage of the ISC/TPS at this rpm? What happens when you drop below it?
I don't have the answers to your questions but I will ask the mechanic. Thanks!

1986 Cougar 3.8 L won't idle.

Reply #27
His alt fuel probably has higher a oxygen content, similar to alcohol, so that the alt fuel brings extra oxygen with it.
What happens if you create a small vacuum leak like disconnecting the PCV valve from the throttle body?
(might be too large a leak, maybe cover with a thumb and let the port bleed a little)

1986 Cougar 3.8 L won't idle.

Reply #28
Quote from: TheFoeYouKnow;465441
His alt fuel probably has higher a oxygen content, similar to alcohol, so that the alt fuel brings extra oxygen with it.
What happens if you create a small vacuum leak like disconnecting the PCV valve from the throttle body?
(might be too large a leak, maybe cover with a thumb and let the port bleed a little)


Any type fuel will start the car up when manually introduced to the TBI - I've used carb. cleaner, starter fluid and 93 octane raw gas. Could bad gas in the tank cause the idling problem?
Haven't tried removing the PCV valve to create a vacuum leak.